Collaborative Research: Evaluating the Tempo, Size, and Chemical Connectivity of Magma Batches in a Tilted Plutonic Complex

合作研究：评估倾斜深成杂岩中岩浆批次的速度、大小和化学连通性

• 批准号: 0838342
• 负责人: Aaron Yoshinobu
• 金额: $ 28.71万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-15 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838342&HistoricalAwards=false
• 关键词: Collaborative; Research; Evaluating; Tempo; Size

Intellectual Merit. In the realm of magmatic arc studies, fundamental gaps exist in our understanding of how individual pulses of magma may physically and chemically interact with extant magma/rock in a growing pluton, how emplacement depth affects the crystallization history and longevity of distinct compositional zones within a vertically-extensive pluton; and (c) whether large, vertically-extensive plutons may form as single, well-mixed open-system reservoirs. The tilted, 15-km thick Wooley Creek batholith-Slinkard pluton system will be examined to test two central hypotheses: (1) pluton construction was via multiple increments of magma with little to no physical and chemical communication at the site of emplacement (i.e., isolated batches); and (2) the upper portions of the system represent a large volume of well-mixed magma at the site of emplacement (i.e., ?big tank?). Field study, high-precision U/Pb analyses, petrography, in situ oxygen isotopic analysis, and LA-ICPMS trace element microanalysis will be utilized to test these hypotheses. The objectives of this research are to (i) delineate the timescale of intrusion, crystallization and solidification; (ii) evaluate the possibility that recharge of mafic magmas remobilized existing crystal mushes; (iii) test the hypothesis that open system processes (e.g., including magma mixing and assimilation) occurred in a large volume, vertically-extensive magmatic system; and (iv) test the hypothesis that magmatic fabrics in plutons form diachronously and reflect the regional tectonic strain field during crystallization. The focus site is a near-ideal system to attain these objectives because (a) the intrusion displays vertical compositional zonation from structurally lower gabbro/diorite upward through quartz diorite, tonalite, granodiorite and granite; (b) co-magmatic compositional links between various phases have been previously established; (c) distinctive lithology, isotopic composition, and ages for the country rocks make it possible to investigate spatial variations in physical & chemical contamination within the magmatic system; (d) magmatic fabrics cross-cut compositional zones; (e) fine-grained dikes in the ?roof zone? represent magmas tapped during construction of the underlying batholith; and (f) the pluton contains minerals (augite, zircon, quartz) whose oxygen isotope and trace element compositions will track upward and lateral variations in magma composition, hence, open-system behavior. This project will test the possible coexistence of discrete large, vertically-extensive magmatic systems having identical crystallization ages and have open-system chemical links from one intrusive phase to another Ie.g., the ?big tank? model). In contrast, an emerging paradigm favors large batholith formation by incremental emplacement of small magma batches, over millions of years, and with distinct pulses with distinct chemical histories. Either outcome will have long-ranging, process-oriented implications for interpreting how large batholiths are constructed in arc settings.Broader Impacts. This project will support undergraduate & graduate student involvement in state-of-the-art analytical and field projects. Results from this work will also be integrated into teaching activities, and because the study area lies in a heavily traveled wilderness area, geologic summaries will be produced for distribution by the U.S. Forest Service to the general public.

智力优点。在岩浆弧研究领域，我们对单个岩浆脉冲如何与生长中的岩体中现存岩浆/岩石发生物理和化学相互作用、侵位深度如何影响结晶历史和不同成分带的寿命的理解存在根本差距。垂直延伸的岩体； (c) 大型、垂直延伸的岩体是否可以形成单一、混合良好的开放系统储层。将检查倾斜的 15 公里厚的伍利溪岩基 - 斯林卡德岩体系统，以测试两个中心假设：(1) 岩体构造是通过岩浆的多次增量形成的，在就位点几乎没有物理和化学通讯（即，隔离批次）； (2) 系统的上部代表了就位点（即“大水池”）处大量混合良好的岩浆。将利用现场研究、高精度 U/Pb 分析、岩相学、原位氧同位素分析和 LA-ICPMS 痕量元素微量分析来检验这些假设。这项研究的目的是 (i) 描绘侵入、结晶和凝固的时间尺度； (ii) 评估镁铁质岩浆的补给重新激活现有水晶糊的可能性； (iii) 检验开放系统过程（例如，包括岩浆混合和同化）发生在大体积、垂直延伸的岩浆系统中的假设； (iv) 检验岩体中岩浆组构穿时形成并反映结晶过程中区域构造应变场的假设。焦点地点是实现这些目标的近乎理想的系统，因为 (a) 侵入体显示出从结构较低的辉长岩/闪长岩向上穿过石英闪长岩、英闪长岩、花岗闪长岩和花岗岩的垂直成分带； (b) 先前已经确定了不同阶段之间的同岩浆成分联系； (c) 围岩独特的岩性、同位素组成和年龄使得研究岩浆系统内物理和化学污染的空间变化成为可能； (d) 岩浆组构横切成分带； (e) 屋顶区域的细粒堤坝？代表在建造下面的岩基期间开采的岩浆； (f) 岩体含有矿物（辉石、锆石、石英），其氧同位素和微量元素成分将跟踪岩浆成分的向上和横向变化，因此，开放系统行为。该项目将测试离散的大型、垂直延伸的岩浆系统是否可能共存，这些岩浆系统具有相同的结晶年龄，并具有从一个侵入相到另一个侵入相的开放系统化学联系，例如“大储罐”。模型）。 相比之下，一种新兴的范式有利于通过数百万年的小批量岩浆增量侵位来形成大型岩基，并具有具有不同化学历史的独特脉冲。这两种结果都将对解释如何在弧形环境中建造大型基岩产生长期的、面向过程的影响。更广泛的影响。该项目将支持本科生和研究生参与最先进的分析和现场项目。 这项工作的结果也将纳入教学活动，并且由于研究区域位于人迹罕至的荒野地区，因此将制作地质摘要，由美国林务局向公众分发。